I bought a new in the box MB5350 in an outlet store.
Firmware was 2.030.

To avoid firmware updates I checked out "return of information to Canon" and "information about new firmware" during setup.
Connected with a wired LAN, no cloud services installed (but I can print from my smartphone).
Installed the Canon setup cartridges.
Nozzle check was perfect the first time.

The printer behaves as all other Canon printers, it is fast, the standard print quality is very good.
In silent mode - otherwise it is too loud in a normal room - the speed is still much better than an average consumer printer.
One pass duplex scanning is a big advantage.
Registering of the papers is a nuisance for a single user (and why can't you print a nozzle check from cassette 2 where your A4 paper is ).
Very nice printer after all.

After 3 days the refillable cartridges with autoreset chips and ink from octopus-office.de arrived.
Filled them with ink.

Sealed the ink outlets of the OEM carts with alu tape (after priming the head and about 100 pages printed 10g of black and 5g of every color was used).

Removing the carts before they are empty is much easier than all the video's suggest: pull the plug when printing, slide the printhead cart by cart to the inlet groove and lift a small plastic lever (really don't understand why you should turn a plastic wheel inside or use screwdrivers, removing black plate etc).

Powered the printer and loaded the refillable carts one by one following the printer menu.
After a rather long cleaning cycle the nozzle check showed a few lines missing in the BK.
A second cleaning solved this (as with many Canon printers, you can clean the BK and colors separatily from the PC, not from the printer panel).

Colors at first sight are very close to the OEM, a photo on glossy paper is nearly the same, no gloss differences or bronzing, only a tad less yellow.

@palombian - Will be interested to hear your experiences with these carts, I have noticed one thing happens with mine on a long print run...

After a lot of pages (maybe 50+) have been printed in a document sometimes the colours but more often the black start misprinting, like you had a clog. I have dicovered that when you remove the carts, and either open the filler plug or depress the spring loaded outlet port a rush of air is heard. Put back in and they print normal again. This may only be happening on my set of carts but would like to hear how yours behave.

Apart from that the ink is a very close match and even printing A4 test images on cheap photo paper (Lidl) was very impressive quality.

BTW I just refilled mine in the printer by carefully removing the plugs and injecting the ink slowly. The printer does not register the new level, but who cares as it saves a long cleaning cycle

Until now I am very satisfied with the ink, but the cartridges have some disadvantages.

I observed black ink splashes on the first pages of the day, probably dropping from the printhead.
After that I saw that the magenta was very dark.
10 prints of the "cartridge test" color patterns in high quality cleared the the colour.

I thought it was the BK ink seeping overnight in the other ink channels, maybe because the level was higher.
Contacted octopus-office.de, who answered very fast and suggested to remove some black ink.
That was better but now the yellow got contaminated.

I decided to fill the OEM setup BK and was able to fill 65ml and suck out the remaining air - suggesting the setup carts are physically the same as the XL - tranferred the auto reset chip.
The problems with the BK disappeared, nozzle check was perfect every morning, I did not have to do any cleaning.

But now the colours started to contaminate each other.
One day the C in the M, another day in the Y, or both (C had the highest level).
Again, this could be cleared by some prints (I prefer dumping ink on paper, not in the waste pads).

I also tried to calibrate with Colormunki, but the last row of the test charts had a lined pattern, suggesting a flow problem.
Not a big deal, I do not plan to print photo's with it.

My eyes dropped on a new type of refillables in China, where the images suggest that the air inlet is connected (wich is not the case in the regular ones), and ordered a set.
I probably will get tomorrow empty OEM carts for CMY, I will try these first with the ARC's.

I had simlar problems when I first used the carts. Nozzle test prints were all magenbta instead of the three colours and as you say some ink leaks. Interesting that you were able to put the ARC chips on the OEM carts, that's an option for me too, but I don't really want to be checking the weight of the cartridges frequently and disabling the print monitoring if I can help it.

I am filling the ARC carts as recommended - 70ml Blk and 20 for colours.

Changing chips is as easy as it is (was) since long with Canon.
I am now over half of the indicated ink level, and it seems to follow the real level.
Hope the ARC's overestimate to be on the safe side.

If refilling OEM's works, I even plan to have a second set ready filled and transplant the ARC chip when a cart is empty.

Another option is, as you say, disabling ink monitoring and watch the level in transparent carts.
That's why I ordered the new ones (they come with one time chips, but I can as well transfer the ones from the empty OEM carts).
But if I was a Canon engineer, I would have taken measures to avoid printhead damage with disabled ink level.

I received this morning the "new model" refillable PGI-2500 carts from China.

There is still no air inlet (above the ink outlet on the printhead side) as with the Canon carts.
But it is no empty box anymore, there is a flexible bag with a spring inside.
I aspired air through the ink fill hole (the upper one on the back side) and it really collapses.
Underneat this ink fill hole there ist an air inlet (delivered with a plug but should be left open when printing) and kind of a labyrinth.
I don't know the purpose of the odd-shaped channel on the side.

I refilled last Friday the CMY OEM setup carts according to the octopus-office.de instructions.
The setup carts contain 15g of ink (5ml for priming the head - thanks Canon - and 10 ml for half of the XL page count) and I could fill 20ml, the Y even 22 by error.
This suggests the carts are physically the same (since I do not know the weight of a PGI-2500XL cartridge I have to believe the refill instructions of 20ml, although it is not impossible there is an extra 5ml in the XL's too).

To avoid entrance of air I even closed the air inlet with aluminum tape, and the ink outlet immediatily after refilling.
There is - as explained on the octopus site - an extra ventilation inside the cartridge: when pressing on the sides of a fully refilled cart there is some ink seeping in the innards, dripping out the not watertight enclosure (this has no further consequences).

Until now I have no clue about the air and ink flow in the carts. It seems not possible to avoid air entering in the ink bag of the OEM carts after refilling (through the ink outlet without valve, or through the "secondary" ventilation).

But given mine and @Redbrickman's observation that the simple container refillables leak ink into other colours (the Y was very dark), a good working cartridge probably has extra features.

I will see this week how the refilled Canon carts perform, it is not excluded I did not get it right the first time.

@palombian, they look mighty impressive compared to my carts which are just a clear box with two holes in the side compares to yours, the OEM colour carts weight in at 64.5 gm and the black is 103.4 gm, if that’s any help.

I got my refillables from Octopus and they are working without a bother, I checked the cyan ink level the other day and when I printed a nozzle check soon afterwards the cyan was completely missing, next day it was back, air probably got in when I remover the cart.

If your still having trouble with these new carts then get some compatibles from 123ink.nl...